Gallium nitride substrate and manufacturing method of nitride semiconductor crystal

ABSTRACT

A gallium nitride substrate comprising a first main surface and a second main surface opposite thereto, wherein the first main surface is a non-polar or semi-polar plane, a dislocation density measured by a room-temperature cathode luminescence method in the first main surface is 1×104 cm−2 or less, and an averaged dislocation density measured by a room-temperature cathode luminescence method in an optional square region sizing 250 μm×250 μm in the first main plan is 1×106 cm−2 or less.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 14/740,725 filedJun. 16, 2015, allowed, which is a continuation of InternationalApplication PCT/JP2013/083110, filed on Dec. 10, 2013, and designatedthe U.S., and claims priority from Japanese Patent Application2012-275035 which was filed on Dec. 17, 2012, Japanese PatentApplication 2013-072629 which was filed on Mar. 29, 2013, and JapanesePatent Application 2013-114619 which was filed on May 30, 2013, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention is related to a gallium nitride substrate and amanufacturing method for manufacturing a nitride semiconductor crystal.

BACKGROUND ART

Nitride semiconductors represented by gallium nitride (GaN) aresemiconductors composed of nitrides of metal elements classified toGroup 13 in the periodic table, and also called Group III nitridesemiconductors, gallium nitride group semiconductors, etc. The nitridesemiconductor is sometimes represented by compositional formulas such as(B, Al, Ga, In)N, (Al, Ga, In)N, B_(x)Al_(y)Ga_(z)In_(1-x-y-z)N (where,0≤x≤1, 0≤y≤1, 0≤z≤1, 0≤x+y+z≤1), Al_(x)Ga_(y)In_(1-x-y)N (where, 0≤x≤1,0≤y≤1, 0≤x+y≤1).

Doped with impuritys, the nitride semiconductor can be electricallyconductive. O (oxygen), Si (silicon), Ge (germanium), etc. are known asn-type impuritys. Mg (magnesium), Zn (zinc), etc. are known as p-typeimpuritys.

The nitride semiconductor is composed of a wurzite structure classifiedto the hexagonal crystal system.

GaN substrates are manufactured by slicing a bulk GaN crystal grown byHVPE (Hydride Vapor Phase Epitaxy) method (Patent Document 1) orammonothermal method (Patent Document 2, Patent Document 3).

A non-polar or semi-polar GaN substrate can be obtained by a method inwhich a bulk GaN crystal grown along the c-axis on a C-plane sapphiresubstrate or a C-plane GaN substrate is sliced so that the non-polarplane or the semi-polar plane appears as a main surface (Non-PatentDocument 1). This method is not suitable for manufacturing a large-areasubstrate although it is advantageous in that a non-polar or semi-polarGaN substrate with low stacking fault density can be obtained.Therefore, it has been recently studied to manufacture a bulk GaNcrystal by a homo-epitaxial growth that uses a non-polar or semi-polarGaN substrate as a seed (Patent Document 4).

The Patent Document 4 says that the difference of impurity concentrationbetween the GaN crystal to be grown and the seed must be 3×10¹⁸ cm⁻³ orless in order to homo-epitaxially grow the GaN crystal with a stackingfault density of 100 cm⁻¹ or less by using a non-polar or semi-polar GaNsubstrate as a seed. This document does not describe an example forwhich a GaN crystal with a impurity concentration of 4×10¹⁸ cm⁻³ or moreand a stacking fault density of 100 cm⁻¹ or less was homo-epitaxiallygrown on the non-polar GaN substrate.

PRIOR ART REFERENCES Patent Documents

-   PD 1: International Publication WO 99/23693-   PD 2: International Publication WO 2002/101125-   PD 3: Japanese Unexamined Patent Application Publication No.    JP-T-2006-509710-   PD 4: Japanese Laid-open Patent Publication No. JP-A-2012-066983

Non-Patent Document

-   NPD 1: Kenji Fujito, et al., phys. stat. sol. (a) 205 (2008) 1056

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

When a nitride semiconductor crystal is epitaxially grown on a non-polaror semi-polar GaN substrate, stacking fault newly formed in the crystalor inherited from the GaN substrate to the crystal deterioratesproperties of semiconductor devices composed of the crystal.

Accordingly, a main object of the present invention is to provide anon-polar or semi-polar GaN substrate having a main surface on which asemiconductor crystal with low stacking fault density can be grown, anda technology necessary for manufacturing the substrate.

Means for Solving the Problems

The present inventors have completed the invention by finding that basalplane dislocation appeared on the main surface of a non-polar orsemi-polar GaN crystal is involved with the generation of stacking faultin a nitride semiconductor crystal to be grown on the main surface.

According to the first aspect of the present invention, there isprovided a gallium nitride substrate and a method for manufacturing anitride semiconductor crystal, including:

(a1) a gallium nitride substrate having a first main surface and asecond main surface opposite thereto, wherein the first main surface isa non-polar or semi-polar plane, and averaged basal plane dislocationdensity in an optional square region sizing 250 μm×250 μm in the firstmain plan is 1×10⁶ cm⁻² or less;(a2) the gallium nitride substrate according to (a1), wherein basalplane dislocation density in the first main surface is 1×10⁴ cm⁻² orless;(a3) the gallium nitride substrate according to (a2), wherein the basalplane dislocation density in the first main surface is 10 cm⁻² or less;(a4) the gallium nitride substrate according to (a2) or (a3), whereinaveraged basal plane dislocation density in an optional square regionsizing 250 μm×250 μm in the first main plan is 1×10⁴ cm⁻² or less;(a5) the gallium nitride substrate according to any one of (a1) to (a4),wherein the area of the first main surface is 1.0 cm² or more;(a6) the gallium nitride substrate according to any one of (a1) to (a5),wherein stacking fault density in the first main surface is 10 cm⁻¹ orless;(a7) the gallium nitride substrate according to any one of (a1) to (a6),wherein the first main surface is an M-plane;(a8) the gallium nitride substrate according to any one of (a1) to (a7),wherein the first main surface is a surface exposed by removing adamaged layer formed by slicing processing;(a9) a method for manufacturing a nitride semiconductor crystal,comprising the crystal growth step of growing a nitride semiconductorcrystal on the first main surface of the gallium nitride substrateaccording to any one of (a1) to (a8);(a10) the method according to (a9), wherein at the crystal growth step,the nitride semiconductor crystal is grown by a vapor phase growthmethod;(a11) the method according to (a10), wherein the vapor phase epitaxymethod is HVPE method;(a12) the method according to (a11), wherein a bulk nitridesemiconductor crystal is grown at the crystal growth step;(a13) the method according to (a10), wherein the vapor phase epitaxymethod is MOCVD method;(a14) the method according to (a13), wherein a thin film of the nitridesemiconductor crystal is grown at the crystal growth step; and(a15) the method according to any one of (a9) to (a14), wherein thenitride semiconductor crystal grown directly on the first main surfaceat the crystal growth step is a GaN crystal.

According to the second aspect of the present invention, there isprovided a gallium nitride substrate and a method for manufacturing anitride semiconductor crystal, including:

(b1) a gallium nitride substrate having a first main surface and asecond main surface opposite thereto, wherein the first main surface isa M-plane, carrier density is 3×10¹⁸ cm⁻³ or more, and stacking faultdensity in the first main surface is 100 cm⁻¹ or less;(b2) the gallium nitride substrate according to (b1), wherein thecarrier density is 4×10¹⁸ cm⁻³ or more;(b3) the gallium nitride substrate according to (b2), wherein thecarrier density is 5×10¹⁸ cm⁻³ or more;(b4) the gallium nitride substrate according to any one of (b1) to (b3),wherein oxygen concentration is 4×10¹⁸ cm⁻³ or more;(b5) a gallium nitride substrate having a first main surface and a thesecond main surface opposite thereto, wherein the first main surface isan M-plane, oxygen concentration is 4×10¹⁸ cm⁻³ or more, and thestacking fault density in the first main surface is 100 cm⁻¹ or less;(b6) the gallium nitride substrate according to (b4) to (b5), whereinthe variation of the oxygen concentration in a plane parallel to thefirst main surface is less than five times of the oxygen concentration;(b7) the gallium nitride substrate according to any one of (b1) to (b6),wherein the stacking fault density is 50 cm⁻¹ or less;(b8) the gallium nitride substrate according to (b7), wherein thestacking fault density is 10 cm⁻¹ or less;(b9) the gallium nitride substrate according to any one of (b1) to (b8),wherein averaged basal plane dislocation density in an optional squareregion sizing 250 μm×250 μm in the first main surface is 1×10⁶ cm⁻² orless;(b10) the gallium nitride substrate according to any one of (b1) to(b9), wherein the area of the first main surface is 1.0 cm² or more;(b11) the gallium nitride substrate according to any one of (b1) to(b10), wherein an angle between the growth direction of the galliumnitride crystal constituting the substrate and the <10-10> direction ofthe crystal is from 0 to 10;(b12) a manufacturing method for manufacturing a semiconductor device,comprising the step of epitaxially growing a nitride semiconductor onthe gallium nitride substrate according to any one of (b1) to (b11); and(b13) the manufacturing method according to (b12) which is a method formanufacturing a semiconductor light-emitting device.

Effect of the Invention

There is provided a non-polar or semi-polar GaN substrate having a mainsurface on which a nitride semiconductor crystal with low stacking faultdensity can be epitaxially grown, and a technology necessary formanufacturing the crystal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts shapes that single crystalline substrate or compositesubstrates usually have, wherein FIG. 1(a) is a perspective view of acircular plate, and FIG. 1(b) is a perspective view of a plate that hasrectangular main surfaces.

FIG. 2 is a conceptual diagram of crystal growth apparatus used in theHVPE method.

FIG. 3 is a conceptual diagram of a crystal growth apparatus used in theammonothermal method.

FIG. 4 is a schematic diagram illustrating the growth of a GaN crystalon the −C-plane (N polar plane) of a C-plane GaN substrate on which amask pattern having a line-shaped opening is formed.

FIG. 5 is an example of temperature profile that can be adopted for atwo-stage growth method.

FIG. 6 is an example of temperature profile that can be adopted for atwo-stage growth method.

FIG. 7 is an example of temperature profile that can be adopted for atwo-stage growth method.

FIG. 8 is a cross-sectional view depicting an exemplary structure of asemiconductor light-emitting device that can be manufactured by usingthe GaN substrate.

FIG. 9 is a cross-sectional view depicting an exemplary structure of asemiconductor light-emitting device that can be manufactured by usingthe GaN substrate.

FIG. 10 is a schematic diagram for explaining a structure of a GaN layerbonded substrate.

FIG. 11 is a cross-sectional view depicting two seed substrates arrangedon a susceptor.

MODE FOR CARRYING OUT THE INVENTION

The surface of a nitride semiconductor single crystal is, herein,separated into a polar plane, a non-polar plane and a semi-polar plane.

The polar plane collectively means +C- and −C-planes.

The +C-plane means a surface having a normal vector of which angle tothe [0001] direction is from 0 to 10°.

The −C-plane means a surface having a normal vector of which angle tothe [000-1] direction is from 0 to 10′.

For the GaN single crystal, the +C-plane is a Ga polar plane and the−C-plane is a N polar plane.

The non-polar plane collectively means M- and A-planes.

The M-plane means a surface having a normal vector of which angle to the<10-10> direction is from 0 to 10°.

The A-plane means a surface having a normal vector of which angle to the<11-20> direction is from 0 to 10°.

The semi-polar plane means a surface that corresponds to neither thepolar plane nor the non-polar plane. The semi-polar planes include, butare not limited to, surfaces having normal a vector parallel to adirection selected from <30-31> direction, <30-3-1> direction, <20-21>direction, <20-2-1> direction, <20-1-1> direction, <10-11> direction,<10-1-1> direction, <10-12> direction, <10-1-2> direction, <10-13>direction, <10-1-3> direction, <11-21> direction, <11-2-1> direction,<11-22> direction, <11-2-2> direction, <11-23> direction and <11-2-3>direction.

FIG. 1 depicts shapes which single crystalline substrates such as a GaNsubstrate and a sapphire substrate, and composite substrates such as aGaN template usually have.

In FIG. 1(a), the shape of the substrate 1 is a circular plate, i.e. aplate having circular main surfaces. In FIG. 1(b), the substrate 1 is aplate having rectangular main surfaces. In respective examples of FIGS.1(a) and (b), the substrate 1 has two main surfaces 11 parallel to eachother and an edge surface 12. Chamfering can be performed, as necessary,for smoothening the boundary between the main surfaces 11 and the edgesurface 12. In addition, although not formed in the each example of FIG.1, an orientation flat to indicate the crystal orientation and an indexflat to distinguish the two sides can be formed as necessary on thesubstrate.

The non-polar GaN substrate means, herein, a GaN substrate having mainsurface which is non-polar plane. In addition, the semi-polar GaNsubstrate means a GaN substrate having main surface which is semi-polarplane.

The M-plane GaN substrate mentioned herein means a GaN substrate havingmain surface which is the M-plane. Accordingly, the M-plane substratesinclude an on-axis substrate having a normal line of the main surface ofwhich the angle to the <1-100> direction of the GaN crystal is 0° and anoff-angle substrate having a normal line of the main surfaces of whichthe angle to the <1-100> direction of the GaN is 10° or less.

The C-plane GaN substrate mentioned herein means a GaN substrate havingmain surface which is the C-plane. Accordingly, the C-plane substratesinclude an on-axis substrate having a normal line of the main surface ofwhich the angle to the [0001] direction of the GaN crystal is 0° and anoff-angle substrate having a normal line of the main surface of whichthe angle to the [0001] direction of the GaN is 10° or less.

One of the main surfaces of the C-plane GaN substrate is the +C-planeand the other is the −C-plane due to intrinsic properties of the GaNcrystal.

[1] First Aspect 1. Non-Polar or Semi-Polar GaN Substrate

According to the first aspect of the present invention, there isprovided a non-polar or semi-polar GaN substrate having a first mainsurface and a second main surface opposite thereto, wherein the firstmain surface is a non-polar or a semi-polar plane, and averaged basalplane dislocation density in an optional square region sizing 250 μm×250μm in the first main plan is 1×10⁶ cm⁻² or less (Embodiment 1).

However, when a damaged region with high fault density in the outer edgeof the first main surface is formed due to machine processing, the basalplane dislocation density of the first main surface is calculated afterexcluding such a damaged region (the same is true when the basal planedislocation density of the first main surface is mentioned hereinafter).

Basal plane dislocation density can be measured by a transmissionelectron microscope (TEM), SEM-CL method (a method combining a scanningelectron microscope and cathode luminescence), a method which uses anAFM or an optical microscope to observe pits formed by etching a samplesurface, etc.

In the non-polar or semi-polar GaN substrate according to Embodiment 1,basal plane dislocation density averaged over the whole of the firstmain surface is preferably 7×10⁵ cm⁻² or less, 5×10⁵ cm⁻² or less, 2×10⁵cm⁻² or less, 1×10⁵ cm⁻² or less, 1×10⁴ cm⁻² or less, 1×10³ cm⁻² orless, and 10 cm⁻² or less, and even 0 cm⁻².

When the basal plane dislocation density averaged over the whole of thefirst main surface is 1×10⁴ cm⁻² or less, averaged basal planedislocation density in an optional square region sizing 250 μm×250 μm inthe first main surface is preferably 1×10⁴ cm⁻² or less.

In the non-polar or semi-polar GaN substrate according to Embodiment 1,the basal plane dislocation density averaged over the whole of the firstmain surface is preferably 10 cm⁻¹ or less, more preferably 5 cm⁻¹ orless, and even preferably 1 cm⁻¹ or less. The stacking fault appeared inthe main surface of the substrate propagates to a nitride semiconductorcrystal epitaxially grown on the main surface.

The stacking fault density of non-polar or semi-polar GaN substrate canbe evaluated by low temperature cathode luminescence (LTCL) method witha sample cooled by liquid nitrogen. By room temperature cathodeluminescence method, the stacking fault density cannot be evaluated.

In the non-polar or semi-polar GaN substrate according to Embodiment 1,the basal plane dislocation density of the second main surface oppositeto the first main surface is not particularly limited.

The GaN substrate according to Embodiment 1 may contain non-metalelements in the first or second period of the periodic table, other thannitrogen (N) and noble gas elements (He and Ne), i.e. hydrogen (H),carbon (C), oxygen (O) and fluorine (F). The sum of the concentrationsof these elements may exceed 1×10¹⁷ cm⁻³, but is desirably 1×10²⁰ cm⁻³or less.

The GaN substrate according to Embodiment 1 may contain silicon (Si), ofwhich the concentration may be 1×10¹⁷ cm⁻³ or more, and even 5×10¹⁷ cm⁻³or more. The silicon concentration of the GaN substrate according toEmbodiment 1 is preferably 1×10¹⁹ cm⁻³ or less.

For the GaN substrate according to Embodiment 1, alkali metalconcentration is preferably low. The alkali metal concentration of theGaN substrate according to Embodiment 1 is preferably 1×10¹⁷ cm⁻³ orless, 5×10¹⁶ cm⁻³ or less, 1×10¹⁶ cm⁻³ or less, and even 1×10¹⁵ cm⁻³ orless.

The GaN substrate according to Embodiment 1 may contain a point defect.

In the GaN substrate according to Embodiment 1, the area of the firstmain surface is usually 1 cm² or more, preferably 2 cm² or more, morepreferably 5 cm² or more, and may be 10 cm² or more.

2. Manufacturing Method of Non-Polar or Semi-Polar GaN Substrate

The GaN substrate according to Embodiment 1 can be manufactured by aprocedure including, but not limited to, the followings:

(i) using a C-plane GaN template as seed to grow a GaN crystal by theHVPE method and processing the GaN crystal to fabricate a C-plane GaNsubstrate (primary substrate);(ii) using the primary substrate as a seed to grow a GaN crystal by theammonothermal method and processing the GaN crystal to fabricate anM-plane GaN substrate (secondary substrate); and(iii) using the secondary substrate as a seed to grow a GaN crystal bythe ammonothermal method and processing the GaN crystal to fabricate anon-polar or semi-polar GaN substrate (the GaN substrate according toEmbodiment 1).

Each step will now be detailed.

2.1 Fabrication of Primary Substrate (C-Plane GaN Substrate)

The GaN crystal for the primary substrate is grown by the HVPE method,using a C-plane GaN template as a seed, the template having a surface ofGaN layer on which a mask pattern for selective growth has previouslyformed.

The C-plane GaN template is a composite substrate having a singlecrystalline GaN layer c-axis-grown on one of the main surfaces of a basematerial which is a crystalline substrate with a chemical compositiondifferent from GaN. The surface of the single crystalline GaN layer isthe +C-plane of GaN.

The base material of the C-plane GaN template is a sapphire substrate, aSiC substrate, a Si substrate, a Ga₂O₃ substrate, an AlN substrate, etc.The single crystalline GaN layer is formed by the MOCVD method, and thelayer thickness is, for example, from 0.5 to 100 μm.

The mask pattern is formed from a material which prohibits the vaporphase growth of GaN, such as silicon nitrides (SiN_(x)) and siliconoxide (SiO₂).

A preferable example of the mask pattern is a stripe pattern(line-and-space pattern). The line width (mask width) in the stripepattern can be from 20 μm to 100 μm, and the space from 200 μm to 3000μm. The direction of the stripe is oriented parallel to the m-axis ofthe single crystalline GaN layer.

The growth of the GaN crystal by the HVPE method can be performed byusing apparatus of which conceptual diagram is depicted in FIG. 2.

The crystal growth apparatus 2 depicted in FIG. 2 is equipped with agrowth furnace 200, introduction tubes 201 to 205 for introducing gasesinto the growth furnace, a reservoir 206 for holding metallic gallium, aheater 207 disposed in such a way that it surrounds the growth furnace,a susceptor 208 for being surmounted by a seed substrate, an exhausttube 209 for exhausting the gasses out of a growth furnace.

The growth furnace 200, the introduction tubes 201 to 205, the reservoir206 and the exhaust tube 209 are preferably made of quartz. Thesusceptor 208 is preferably made from carbon, and in particular, thesurface thereof is preferably coated with SiC.

Gasses G1, G2, G4 and G5 introduced via the introduction tube 201, 202,204 and 205 into the growth furnace 200 are ammonia (NH₃), carrier gas,shielding gas, doping gas, and so on. Hydrogen chloride (HCl) fed viathe introduction tube 203 into the reservoir 206 reacts with metallicgallium held by the reservoir and generates gaseous gallium chloride(GaCl). As HCl is usually diluted with the carrier gas before being fedinto the reservoir 206, the gas G3 introduced via the reservoir into thegrowth furnace contains GaCl, HCl and the carrier gas.

Gasses preferably used as the carrier gas or the shielding gas arehydrogen gas (H₂) and nitrogen gas (N₂).

GaN generated by the reaction of GaCl with NH₃ in the growth furnace 200is epitaxially grown on the seed substrate.

Substrate temperature during the crystal growth can be appropriatelyadjusted preferably within the range from 900 to 1200° C.

Pressure in the growth furnace during the crystal growth can beappropriately adjusted preferably within the range from 50 to 120 kPa.

The susceptor 208 is preferably rotated so that the crystal is grownuniformly on the seed substrate. The rotational rate can be, forexample, from 1 to 50 rpm.

Crystal growth rate can be adjusted, for example, within the range from80 to 300 μm/h. The partial pressure of GaCl or NH₃ or both can beincreased to increase the growth rate. The GaCl partial pressure ispreferably from 2×10² to 2×10³ Pa. The NH₃ partial pressure ispreferably from 4×10³ to 1×10⁴ Pa.

The partial pressure of a gas mentioned here means a value (P×r) whichis a pressure (P) in a growth furnace multiplied by the ratio (r) of avolumetric flow rate of the gas to the sum of those of all the gassesfed into the growth furnace. The same is true when the gas partialpressure in the growth furnace in the HVPE method is mentionedhereinafter.

After processing the outer shape of the bulk GaN crystal grown by theHVPE method into an appropriately shape, necessary processings, such asslicing processing, removal of a damaged layer by surface etching andplanarization of the main surface are performed to fabricate a C-planeGaN substrate. The −C-plane (N-polar plane) to be used for epitaxialgrowth at the next step is finished by CMP (Chemical MechanicalPolishing).

2.2 Fabrication of Secondary Substrate (M-Plane GaN Substrate)

A GaN crystal for the secondary substrate is grown by using the primarysubstrate (C-plane GaN substrate) as a seed by the ammonothermal method.Prior to the growth step, a mask pattern for selective growth is formedon the −C-plane (N-polar plane) of the primary substrate.

On the mask pattern, a line-shaped opening of about 100 μm in width isformed, which is oriented parallel to the a-axis of GaN. The mask isformed of a metal insolvable or indecomposable during the GaN crystalgrowth by the ammonothermal method, for example, Al, W, Mo, Ti, Pt, Ir,Ag, Au, Ta, Ru, Nb, Pd, and the alloy thereof.

A feedstock for GaN to be grown on the seed is preferably, but notlimited to, polycrystalline GaN, but it may contain metallic gallium(zero-valent gallium). Usable polycrystalline GaN is the one that ismanufactured by a method for reacting metallic gallium, gallium oxide,gallium hydroxide, etc. with ammonia, or reacting metallic gallium withnitrogen under a high temperature and pressure condition. Theconcentration of oxygen contained as a impurity in polycrystalline GaNis usually 5×10²⁰ cm⁻³ or less, preferably 1×10²⁰ cm⁻³, or less, andmore preferably 5×10¹⁹ cm⁻³ or less.

The amounts of impuritys, such as water and oxygen, contained in ammoniaused as a solvent are preferably 10 ppm or less, more preferably 0.1 ppmor less.

A mineralizer containing halogen elements, such as ammonium halide,gallium halide, and hydrogen halide can be preferably used. The purityof the mineralizer is preferably 99% or more, more preferably 99.99% ormore.

The GaN crystal growth by the ammonothermal method can be performed withthe apparatus explained by the conceptual diagram depicted in FIG. 3.

In the crystal growth apparatus 3 depicted in FIG. 3, the crystal growthis performed in a cylindrical growth vessel 320 loaded into acylindrical autoclave 301. The growth vessel 320 has a crystal growthzone 306 and a feed stock dissolution sone 309 which are divided fromone another by a baffle 305 therein. A seed crystal 307 is set suspendedby a platinum wire 304 in the crystal growth zone 306. A feedstock 308is loaded into the feedstock dissolution zone 309.

Gas supply lines connected to a vacuum pump 311, an ammonia tank 312 anda nitrogen tank 313 are connected via a valve 310 to the autoclave 301.During charging the growth vessel 320 with ammonia, a mass flow meter314 can be used to confirm the amount of ammonia fed from the ammoniatank 312.

During the crystal growth, the growth vessel 320 encapsulating the seedcrystal, the feedstock, the mineralizer and the solvent is loaded intothe autoclave 301, and in addition, the space between the autoclave 301and the growth vessel 320 is filled with the solvent, and then, theautoclave 301 is sealed. Then, the whole of the autoclave 301 is heatedby a heater (not depicted) until an ultra-critical or sub-critical stateis achieved in the growth vessel 320.

Pressure in the growth vessel 320 during the crystal growth is usually120 MPa or more, preferably 150 MPa or more, more preferably 180 MPa ormore, and usually 700 MPa or less, preferably 500 MPa or less, morepreferably 350 MPa or less, and may be even 300 MPa or less.

Temperature in the growth vessel 320 during the crystal growth isusually 500° C. or more, preferably 515° C. or more, more preferably530° C. or more, and usually 700° C. or less, preferably 650° C. orless, more preferably 630° C. or less.

Temperature in the feedstock dissolution zone 309 is higher than that inthe crystal growth zone 306. The temperature difference between thefeedstock dissolution zone and the crystal growth zone is preferably 5°C. or more, more preferably 10° C. or more, and preferably 100° C. orless, more preferably 80° C. or less.

On the −C-plane of the primary substrate, as schematically depicted inFIG. 4, a plate-like GaN crystal of which thickness direction is them-axis direction is grown from the opening of the mask pattern.

The secondary substrate (M-plane GaN substrate) is cut out of this GaNcrystal. The main surface to be used for epitaxial growth at the nextstep is planarized by lapping and subsequent CMP. In order to completelyremove by CMP a damaged layer introduced by slicing processing andlapping, cross-sectional SEM-CL observation of a GaN crystal sliced andlapped under the same condition is performed, and the approximatethickness of the damaged layer to be removed is previously examined,which thickness is taken into account to determine the amount to beremoved by CMP.

2.3 Fabrication of Non-Polar or Semi-Polar GaN Substrate

The GaN crystal is grown by the ammonothermal method by using thesecondary substrate (M-plane GaN substrate) as a seed.

A feedstock, a solvent and mineralizers preferably used in theammonothermal method are the same as those for growing the GaN crystalof the secondary substrate. Available crystal growth apparatus and apreferable condition during the crystal growth are also the same asthose for growing the GaN crystal of the secondary substrate.

A non-polar or semi-polar GaN substrate according to Embodiment 1 is cutout of the GaN crystal grown on the secondary substrate. Slicing thecrystal in parallel to the main surface of the secondary substrate canprovide an M-plane GaN substrate. Slicing in other directions canprovide GaN substrates having a non-polar plane or various semi-polarplanes as a main surface other than the M-plane.

After the slicing processing, at least one main surface is lapped andsubsequently planarized by CMP. In order to completely remove by CMP adamaged layer introduced by slicing processing and lapping,cross-sectional SEM-CL observation of a GaN crystal sliced and lappedunder the same condition is performed, and the approximate thickness ofthe damaged layer to be removed is previously examined, which thicknessis taken into account to determine the amount to be removed by CMP.

3. Use Application of Non-Polar or Semi-Polar GaN Substrate

On the first main surface with low basal plane dislocation density ofthe GaN substrate according to Embodiment 1, a nitride semiconductorcrystal with low stacking fault density and high quality can be formedby epitaxial growth.

The non-polar or semi-polar GaN substrate according to Embodiment 1 andthe nitride semiconductor layer grown directly on the first main surfaceof the substrate preferably satisfy the condition of lattice mismatchrepresented by the following formula (1):

2|a ₁ −a ₂|/[a ₁ +a ₂]≤1×10⁻³  (1),

where a₁ and a₂ are lattice constants of cryatal axises parallel to thefirst main surface, of GaN and the nitride semiconductor layer,respectively.

The lattice mismatch is preferably 5×10⁻⁴ or less, more preferably1×10⁻⁴ or less, and in particular, preferably 1×10⁻⁵ or less.

Various semiconductor device structures can be formed on the first mainsurface of the GaN substrate according to Embodiment 1 by the epitaxialgrowth of nitride semiconductor. Specific examples include lightemitting devices such as light-emitting diodes, and laser diodes;electron devices such as rectifiers, bipolar transistors, field effecttransistors, and HEMTs (High Electron Mobility Transistors);semiconductor sensors such as temperature sensors, pressure sensors,radiation sensors, and visible-ultraviolet photodetectors; SAW (SurfaceAcoustic Wave) devices, vibrators, resonators, oscillators, MEMS (MicroElectro Mechanical System) elements, and voltage actuators.

A bulk GaN crystal can also be epitaxially grown on the first mainsurface of the GaN substrate according to Embodiment 1. In other word,the GaN substrate according to Embodiment 1 can be used as a seed forthe growth of bulk GaN.

[2] Second Aspect 1. M-Plane GaN Substrate

According to the second aspect of the present invention, there isprovided an M-plane GaN substrate having a first main surface and asecond main surface opposite thereto, wherein the first main surface isan M-plane, and the carrier density is 3×10¹⁸ cm⁻³ or more, and stackingfault density in the first main surface is 100 cm⁻¹ or less (Embodiment2a).

According to the second aspect of the present invention, there is alsoprovided an M-plane GaN substrate having a first main surface and asecond main surface opposite thereto, wherein the first main surface isa M-plane, and n-type impurity concentration is more than 4×10¹⁸ cm⁻³ ormore, stacking fault density in the first main surface is 100 cm⁻¹ orless (Embodiment 2b).

Hereinafter, “Embodiment 2” may collectively mean Embodiments 2a and 2b.

In the above described Embodiment 2, the stacking fault density in thefirst main surface means stacking fault density averaged over the wholeof the first main surface. However, when a damaged region with highfault density due to machine processing is formed in the outer edge ofthe first main surface, the stacking fault density of the first mainsurface is calculated after excluding the damaged region (hereinafter,the same is true when the stacking fault density of the first mainsurface is mentioned).

When the carrier density of the GaN substrate is 3×10¹⁸ cm⁻³ or more, anelectrode with low contact resistance can be readily formed on thesurface thereof. When the carrier density of the GaN substrate is 4×10¹⁸cm⁻³ or more, and even 5×10¹⁸ cm⁻³ or more, the electrode with lowcontact resistance can be more readily formed on the surface.

Although no upper limit exists for the carrier density of the M-planeGaN substrate according to Embodiment 2, the density beyond 1×10¹⁹ cm⁻³tends to saturate the reduction effect of the contact resistance to theelectrode. For example, in use application to light emitting devices,carrier density beyond 5×10¹⁹ cm⁻³ is rarely required for the GaNsubstrate.

Elements capable of being added to GaN as impuritys can be appropriatelyreferenced in the well-known art and preferably include, but are notlimited to, oxygen (O) and silicon (Si). Only one of oxygen and silicon,or both may be used.

In order to obtain a carrier density of 3×10¹⁸ cm⁻³ or more by usingoxygen as a impurity, an oxygen concentration of 4×10¹⁸ cm⁻³ or more isdesirable.

The impurity concentration in the GaN substrate can be measured by SIMS(secondary ion mass spectroscopy), and the carrier density can bemeasured by Raman spectroscopy.

Since the M-plane GaN substrate according to Embodiment 2 has a lowstacking fault density of 100 cm⁻¹ or less in the first main surface, anitride semiconductor film with high quality can be epitaxially grown onthe first main surface by MOCVD (metal organic chemical vapordeposition) method or MBE (molecular beam epitaxy) method.

The stacking fault density in the first main surface is preferably 50cm⁻¹ or less, more preferably 10 cm⁻¹ or less.

The stacking fault density in the M-plane GaN substrate can be evaluatedby low temperature cathode luminescence (LTCL) measurement with a samplecooled by liquid nitrogen. The stacking fault density cannot beevaluated by room temperature cathode luminescence measurement.

2. Manufacturing Method of M-Plane GaN Substrate

The M-plane GaN substrate according to Embodiment 2 can be manufacturedfrom the GaN crystal grown by the HVPE method by using the M-plane GaNsubstrate according to above-mentioned Embodiment 1 as a seed.

When the GaN crystal is grown by using M-plane GaN substrate as a seed,the growth direction thereof is a direction perpendicular to the mainsurface (M-plane) of the substrate. The growth direction here means thethickness direction of the GaN crystal layer grown on the main surfaceof the substrate.

The GaN crystal uniformly doped with oxygen can be obtained by adoptinga condition under which the crystal surface is a mirror surface duringthe growth. The reason is that under such a condition, the M-planeaccounts for the entire crystal surface during the growth. In theM-plane GaN substrate cut out of the GaN crystal grown under such acondition, the variation of oxygen concentration in a surface parallelto the main surface is less than five-fold of the oxygen concentration.

In an example, a plurality of seed substrates can be placed in atile-like arrangement on a susceptor to grow one continuous GaN crystallayer over the substrates.

When the GaN crystal is homo-epitaxially grown on the main surface ofthe M-plane GaN substrate, a larger off-angle of the main surfaceinhibits the generation of stacking fault more. Accordingly, theoff-angle of the main surface of the seed substrate is preferably 2° ormore, and more preferably 5° or more.

The GaN crystal growth by the HVPE method can be performed by using thecrystal growth apparatus depicted in the conceptual diagram of theabove-mentioned FIG. 2.

In particular, a two-stage growth method including (a) a heating step,(b) an initial growth step and (c) a main growth step, which are to bedescribed hereinafter, in the order mentioned can be performed to obtainthe GaN crystal with reduced stacking fault density.

(a) Heating Step

At the heating step, substrate temperature is raised from roomtemperature to T₁ without feeding GaCl onto the seed substrate. T₁ ispreferably 830° C. or more, and 870° C. or less. Heating rate ispreferably 12° C./min or more, and 30° C./min or less. The heating ratemay be constant over the course of the heating step or changed on theway.

At the heating step, atmospheric gasses that can be introduced into thegrowth furnace are H₂, NH₃, N₂, etc., and at least both of NH₃ and N₂are preferably introduced. The volumetric flow rate of NH₃ introducedinto the growth furnace is preferably 15% or more of the sum of thevolumetric flow rates of all the gasses introduced into the growthfurnace.

(b) Initial Growth Step

At the initial growth step, the substrate temperature is raised from T₁to T₂ during the growth of the GaN by feeding GaCl and NH₃ onto thesubstrate. T₂ is preferably 940° C. or more and 1050° C. or less. Theheating rate is preferably 11° C./min or more and 24° C./min or less.

When the pressure in a growth furnace at the initial growth step is1.0×10⁵ Pa, the GaCl partial pressure is preferably 2.0×10² Pa or moreand 5.0×10² Pa or less, and the NH₃ partial pressure is preferably8.0×10³ Pa or more and 1.2×10⁴ Pa or less.

At the initial growth step, N₂ preferably accounts for 70% or more, andeven 90% or more, by volumetric flow rate, of all the gasses introducedinto a growth furnace. H₂ among the other gasses can be introduced intothe growth furnace at the initial growth step.

(c) Main Growth Step

At the main growth step, the GaN crystal is grown into a thick film byfeeding GaCl and NH₃ onto the seed substrate with substrate temperaturekept to be T₂. The pressure in the growth furnace at the main growthstep is preferably 50 kPa or more and 120 kPa or less.

When the pressure in the growth furnace at the main growth step is1.0×10⁵ Pa, the GaCl partial pressure is preferably 2.0×10² Pa or moreand 5.0×10² Pa or less, and the NH₃ partial pressure is preferably8.0×10³ Pa or more and 1.5×10⁴ Pa or less.

At the main growth step, N₂ preferably accounts for 70% or more, andeven 90% or more, by volumetric flow rate, of all the gasses introducedinto a growth furnace. H₂ among the other gasses can be introduced intothe growth furnace at the main growth step.

Temperature profiles adoptable in the above described two-stage growthmethod are depicted in FIGS. 5 to 7.

In the example of FIG. 5, the heating rate is constant from the heatingstep to the initial growth step. In the example of FIG. 6, between theheating step and the initial growth step, the temperature keeping stepof keeping the substrate temperature constant is provided. The period ofthe temperature keeping step can be appropriately set, and is, forexample, one minute or more and 60 minutes or less.

In the example of FIG. 7, the heating rate is changed at the early andlater stages of the initial growth step. In this example, the heatingrate is changed discontinuously, but it can be changed gradually.

At the heating growth step and the main growth step, the GaN crystal canbe grown with doping gasses fed.

Oxygen gas (O₂) or water (H₂O) as doping gasses for oxygen doping, andsilane (SiH₄), disilane (Si₂H₆), chlorosilane (SiH₃Cl), dichlorosilane(SiH₂Cl₂), trichlorosilane (SiHCl₃), tetrachlorosilane (SiCl₄),tetrafluorosilane (SiF₄), etc. as doping gasses for silicon doping canbe preferably used.

Instead of feeding the doping gasses, oxygen-containing gas generatedfrom quartz members configuring crystal growth apparatus such as agrowth furnace, an introduction tube, and a reservoir can be used foroxygen doping of the GaN crystal. A higher temperature of quartz memberduring the crystal growth leads to a greater amount of the generatedoxygen-containing gas and a higher oxygen concentration in the GaNcrystal. When the oxygen concentration in the GaN crystal must be keptlow, the metrology described in above-mentioned Patent Document 4(Japanese Laid-open Patent Publication No. JP-A-2012-066983) can bereferenced. One example is as follows.

1) In the growth furnace, a liner tube made of pBN (pyrolytic boronnitride) is placed, inside which a seed substrate is placed, and therebyoxygen-containing gas generated from the quartz growth furnace isprevented from contacting to the seed substrate.2) In the above described 1), high purity nitrogen gas as a shield gasflowing between the growth furnace and the liner tube can moreeffectively suppress the contact of the oxygen-containing gas generatedfrom the growth furnace to the seed substrate.3) To a susceptor surmounted by a seed substrate, a local heatingmechanism is installed, which, in combination with the heater, is usedto heat the seed substrate. Thus, heater output necessary for heating toa predetermined temperature can be reduced, and the temperature of thequartz members heated together with the seed substrate, such as thegrowth furnace, the introduction tube, the reservoir, can be lowered,and thereby the amount of the oxygen-containing gas generated from thesequartz members can be suppressed.4) Heat shielding means such as a heat shield plate can be used toinhibit heat transfer from the heater to the reservoir, thereby loweringthe temperature of the reservoir, and the amount of oxygen-containinggas generated from the reservoir can be suppressed.

After processed into an appropriate outer-shape, the bulk GaN crystalgrown by the above described two-stage growth method is subjected tonecessary processings, such as slicing processing, removal of a damagedlayer by surface etching and planarization of the main surface. At leastone main surface is planarized by lapping and subsequent CMP. In orderto completely remove by CMP a damaged layer introduced by slicingprocessing and lapping, the approximate thickness of the damaged layerto be removed is previously examined by cross-sectional SEM-CLobservation of a GaN crystal sliced and lapped under the same condition,which thickness is taken into account to determine the amount to besubjected to CMP.

By the above procedure, the objective M-plane GaN substrate can beobtained.

3. Use Application of M-Plane GaN Substrate 3.1 SemiconductorLight-Emitting Device

The GaN substrate according to Embodiment 2 can be preferably used formanufacturing semiconductor light-emitting devices such aslight-emitting diodes (LEDs), laser diodes (LDs).

FIG. 8 depicts an exemplary structure of a semiconductor light-emittingdevice capable of being manufactured by using the GaN substrateaccording to Embodiment 2. FIG. 8 is a cross-sectional view, and thesemiconductor light-emitting device 40A has a semiconductor laminate Lgrown on the main surface of the GaN substrate 41 by MOVPE method (metalorganic vapor phase epitaxy method). The semiconductor laminate Lincludes an n-type layer 42, a light-emitting layer 43 and a p-typelayer 44 in the mentioned order from the side of the GaN substrate 41.The n-type layer 42 is, for example, made of GaN or AlGaN, and dopedwith Si. The light-emitting layer 43 is, for example, formed by stackingalternately In_(x1)Ga_(1-x1)N well layers and In_(x2)Ga_(1-x2)N(0≤x₂<x₁) barrier layers. The p-type layer 44 is, for example, made ofGaN or AlGaN, and doped with Mg.

A positive electrode 45 is formed on the top of the p-type layer 44. Anegative electrode 46 is formed on the surface of the n-type layerexposed by partially etching the laminate.

Decreased stacking fault density of the GaN substrate 41 improves thequality of the semiconductor laminate L grown thereon and therebyincreases the light-emitting efficiency of the semiconductorlight-emitting device 40A.

Since increased n-type carrier density of the GaN substrate 41 lowersthe electric resistance, and thereby the n-type layer 42 and thesubstrate acts as pathways of electric current, the operating voltage ofthe semiconductor light-emitting device 40A is lowered.

For the semiconductor light-emitting device 40B depicted in FIG. 9having a negative electrode 46 on the backside of the GaN substrate 41,the lowering effect of the operating voltage due to the increasedcarrier density of the GaN substrate 41 is more significant. The reasonis that in addition to decrease in the series resistance of the devicedue to decrease in the electric resistance of the GaN substrate 41, thecontact resistance between the negative electrode 46 and the GaNsubstrate 41 decreases due to the increase in the carrier density of GaNsubstrate 41.

3.2 GaN Layer Bonded Substrate

By using the GaN substrate according to Embodiment 2, a GaN layer bondedsubstrate can be manufactured.

A GaN layer bonded substrate is, as schematically depicted in FIG. 10, acomposite substrate in which a GaN layer is bonded to adifferent-composition substrate with a chemical composition differentfrom that of GaN, and can be used for manufacturing semiconductordevices such as light emitting devices.

The GaN layer bonded substrate can be typically manufactured byperforming the first step of implanting ions into the vicinity of themain surface of the GaN substrate, the second step of bonding the mainsurface side of the GaN substrate to a different-composition substrateand the third step of separating the GaN substrate at the ion-implantedregion serving as a boundary to form a GaN layer bonded to thedifferent-composition substrate, in the mentioned order.

Accordingly, the GaN layer bonded substrate manufactured by using theGaN substrate according to Embodiment 2 will have a structure in whichthe GaN layer separated from the GaN substrate according to Embodiment 2is bonded to the different-composition substrate.

The different-composition substrates capable of being used for the GaNlayer bonded substrate are exemplified by sapphire substrates, AlNsubstrates, SiC substrates, ZnSe substrates, Si substrates, ZnOsubstrates, ZnS substrates, quartz substrates, spinel substrates, carbonsubstrates, diamond substrates, Ga₂O₃ substrates, ZrB₂ substrates, Mosubstrates, W substrates, etc.

For the structure of the GaN layer bonded substrate and themanufacturing method and application thereof, Japanese Laid-open PatentPublication No. JP-A-2006-210660, Japanese Laid-open Patent PublicationNo. JP-A-2011-44665, and so on can be referenced.

3.3 Other Use Applications

The M-plane GaN substrate according to Embodiment 2 can be used as asubstrate for manufacturing not only light emitting devices but alsovarious semiconductor devices, for example, electron devices such asrectifiers, bipolar transistors, field effect transistors, HEMTs (HighElectron Mobility Transistors), semiconductor sensors such astemperature sensors, pressure sensors, radiation sensors, andvisible-ultraviolet photodetectors, SAW (Surface Acoustic Wave) devices,vibrators, resonators, oscillators, MEMS (Micro Electro MechanicalSystem) elements, voltage actuators, etc.

[3] Experimental Results 1. Experiment 1 (1) Preparation of PrimarySubstrate (C-Plane GaN Substrate)

A C-plane GaN substrate was prepared, which has a CMP finished −C-plane(N-polar plane) cut out of the GaN crystal grown by the HVPE method onthe C-plane GaN template having a mask pattern formed on the mainsurface thereof.

(2) Fabrication of Secondary Substrate (M-Plane GaN Substrate)

The prepared primary substrate was used as a seed to grow a GaN crystalby the ammonothermal method. The specific procedure is as follows.

(i) Polycrystalline GaN was prepared, which was manufactured as afeedstock by the vapor-phase-reaction of NH₃ with GaCl. Ammoniumfluoride (NH₄F) and hydrogen iodide (HI) were also prepared asmineralizers.

A mask pattern having a line-shaped opening of 100 μm width was formedby using TiW alloy on the −C-plane of the primary substrate to be usedas a seed. The longitudinal direction of the opening was orientedparallel to the a-axis of GaN.

(ii) Polycrystalline GaN and NH₄F were loaded into the lower part(feedstock dissolution zone) of a cylindrical growth vessel made ofPt—Ir alloy. The amount of NH₄F was set so that the mole ratio offluorine atom to NH₃ to be introduced later into the growth vessel was0.5%. Then, a platinum baffle dividing the upper part (crystal growthzone) and lower part of the growth vessel was placed in the growthvessel. After the placement of the baffle, the primary substrate to beused as a seed was placed, with itself kept hung by a platinum wire, inthe crystal growth zone.(iii) A cap made of Pt—Ir with a tube was attached to the upper part ofthe growth vessel by welding and the tube was connected to a gas supplyline. Then, after cooling the lower part of the growth vessel by liquidnitrogen, HI was introduced into the growth vessel via the tube. Theamount of HI was set so that the mole ratio of iodine atom to NH₃ to besubsequently introduced into the growth vessel was 2%.

After introducing HI, the gas supply line was switched and NH₃ wasintroduced into the growth vessel. The amount of NH₃ was set to be about55% of the effective volume of the growth vessel after conversion intothe volume of liquid NH₃ at −33° C.

(iv) After introduction of NH₃, the tube was weld and cut off to sealthe growth vessel, which was then inserted into cylindrical autoclavemade of nickel based alloy with a valve. Then, the space between thegrowth vessel and the autoclave was also charged with NH₃ via the valve,which was then closed to seal the autoclave. The amount of NH₃ forcharging the space was set to be about 56% of the effective volume ofthe growth vessel after conversion into the volume of liquid NH₃ at −33°C.(v) The autoclave was heated from outside by using an electric furnaceequipped with a plurality of independently controllable heaters. Theheaters were controlled so that the averaged temperature of the growthvessel (averaged value of the temperatures of the crystal growth zoneand the feedstock dissolution zone) was 600° C. and the temperaturedifference between the crystal growth zone and the feedstock dissolutionzone was 20° C., and this was maintained for 30 days. In this instance,pressure inside the autoclave was 215 MPa.(vi) 30 days later, NH₃ filling the space between the growth vessel andautoclave was released by opening the valve of the autoclave, and thepressure difference thereby generated between the inside and the outsideof the growth vessel was used to break the growth vessel. Then, afterNH₃ in the growth vessel was confirmed to have also been exhausted, theprimary substrate was taken out.

On the −C-plane of the primary substrate taken out from the growthvessel, from the opening of the mask pattern, a plate-like GaN crystalwas grown, of which the dimension in the c-axis direction was 7 mm andthe thickness direction was the m-axis direction.

Out of this GaN crystal, an M-plane substrate (secondary substrate) wascut, which had rectangular main surfaces having longer sides parallel tothe a-axis and shorter sides parallel to the c-axis, and a size of 35 mm(length)×7 mm (width)×330 μm (thickness). Both of the main surfaces weresubjected to lapping and CMP processing, and a damaged layer formed byslicing was completely removed.

(3) Fabrication of Tertiary Substrate (M-Plane GaN Substrate)

A GaN crystal was grown by the ammonothermal method by using thesecondary substrate fabricated in the above described procedure (M-planeGaN substrate) as a seed.

Except that the seed was different, additive amounts of the mineralizerswere changed so that the mole ratios of fluorine and iodine atoms to NH₃were 0.5% and 1.5%, respectively, and the crystal growth time period was20 days, the GaN crystal for the tertiary substrate was grown in thesame procedure as that of the GaN crystal growth for the secondarysubstrate.

The size of the GaN crystal obtained after the growth for 20 days was 40mm (a-axis direction)×10 mm (c-axis direction)×6 mm (m-axis direction).

Out of this GaN crystal, an M-plane substrate with an off-angle(tertiary substrate) was cut, which had rectangular main surfaces havinglonger sides parallel to the a-axis and shorter sides parallel to thec-axis, and a size of 17 mm (length)×8 mm (width)×330 μm (thickness).The off-angle was set to be −2° in the [0001] direction, and within±0.1° in the [−12-10] direction. Both of the main surfaces weresubjected to lapping and CMP processing, and a damaged layer formed byslicing was completely removed.

SIMS analysis of the M-plane GaN substrate determined hydrogenconcentration to be 1.4×10¹⁸ cm⁻³, oxygen concentration 8.7×10¹⁸ cm⁻³and fluorine concentration 7×10¹⁷ cm⁻³. Analysis by the room-temperaturecathode luminescence method (3 kV, 100 pA, 1000-fold magnification) didnot detect basal plane dislocation. Analysis by the low-temperaturecathode luminescence method (10 kV, 4 nA, field of view at 200-foldmagnification, sample temperature 82K) determined the stacking faultdensity of the substrate to be 0 cm⁻¹.

In these measurements, observed regions per field of view were 90 μm×120μm for field of view at 1000-fold magnification and 600 μm×400 μm forfield of view at 200-fold magnification.

(4) GaN Crystal Growth by the HVPE Method

A GaN crystal was grown by the HVPE method by using the tertiarysubstrate fabricated in the above described procedure (M-plane GaNsubstrate) as a seed.

For the GaN crystal growth, the above-mentioned two-stage growth methodwas used. In other words, the susceptor placed in the growth furnace wassurmounted by the seed substrate so that one main surface of thesubstrate turned up, and then, the substrate temperature was raised upto 850° C. with only N₂ and NH₃ initially fed onto the seed substrate(heating step), and the temperature was kept for 15 minutes.

Then, feeding GaCl onto the seed substrate was initiated by feeding HCldiluted with N₂ into the reservoir heated to 800° C. which holdedmetallic gallium, and the substrate temperature was raised at a rate of21° C./min (initial growth step).

After the substrate temperature reached 950° C., the substratetemperature was kept constant while GaN crystal was grown for 20 hoursby feeding GaCl and NH₃ onto the seed substrate (main growth step).

From the start of the heating step to the end of the main growth step,the pressure in the growth furnace was controlled to be 1.0×10⁵ Pa, theGaCl partial pressure 3.1×10² Pa and the ammonia partial pressure9.8×10³ Pa. For carrier gasses, N₂ and H₂ were used, and the ratio of N₂was set so as to account for 48% of the sum of volumetric flow rates ofall the gasses fed into the growth furnace.

The grown GaN crystal covered a main surface of the tertiary substratelike a film, and the thickness was about 0.8 mm.

Analysis of the as-grown GaN crystal film by the room-temperaturecathode luminescence method (3 kV, 100 pA, 1000-fold magnification)determined basal plane dislocation density to be 9.4×10⁵ cm⁻².

Analysis of the as-grown GaN crystal film by the low-temperature cathodeluminescence method (acceleration voltage 5 kV, electric current 500 pA,field of view at 200-fold magnification, sample temperature 82K) did notdetect stacking fault.

Oxygen concentration measured by SIMS analysis of the as-grown GaNcrystal film was 4.0×10¹⁸ cm⁻³, and carrier density in the vicinity ofthe main surface measured by Raman spectroscopy was 2.5×10¹⁸ cm⁻³.

This oxygen concentration value was lower than the oxygen concentrationof the tertiary substrate used as a seed (8.7×10¹⁸ cm⁻³), and thedifference was 4.7×10¹⁸ cm⁻³.

Oxygen contained in the GaN crystal film was attributed to oxygencompounds such as H₂O incorporated into the feedstock, or to quartzmembers configuring the vapor phase epitaxy apparatus.

2. Experiment 2 (1) Fabrication of Primary Substrate (C-Plane GaNSubstrate)

A C-plane GaN template having a single crystalline GaN layer grown on aC-plane sapphire substrate was prepared, and a mask pattern was formedon the surface of the GaN layer by using a silicon nitride film of 80 nmthickness. Plasma CVD method was used for the formation of the siliconnitride film, and photo-lithography and dry etching techniques were usedfor the patterning.

The mask pattern was configured to be a stripe pattern (line-and-spacepattern) of 850 μm pitch with 50 μm line width (mask width) and 800 μmspace width, and the stripe was oriented parallel to the direction ofthe m-axis of the single crystalline GaN layer.

On the C-plane GaN template with the above described mask patternformed, an undoped GaN crystal was grown by the HVPE method. For 15minutes from the start of the growth, the substrate temperature was keptto be 970° C., and then, raised to 1020° C. while the growth wascontinued. The pressure in the growth furnace during the growth wascontrolled to be 1.0×10⁵ Pa, the GaCl partial pressure 7.4×10² Pa, andthe ammonia partial pressure 1.1×10⁴ Pa. The growth time was set to be55 hours.

A C-plane substrate (primary substrate) of 330 μm thickness was cut outof the thus grown GaN crystal. The −C-plane was subjected to lapping andCMP processing to completely remove a damaged layer formed by slicing.

(2) Fabrication of Secondary Substrate (M-Plane Substrate)

After a mask pattern having a line-shaped opening of 100 μm widthparallel to the a-axis of GaN is formed with TiW alloy on the −C-planeof the C-plane GaN substrate fabricated by the above describedprocedure, a GaN crystal was grown by an ammonothermal method by usingthe C-plane GaN substrate as a seed.

The growth of the GaN crystal by the ammonothermal method and thefabrication of the tertiary substrate (M-plane substrate) from the GaNcrystal were performed in the same manner as the method described in (2)of the Experiment 1 except that the additive amounts of the mineralizerswere changed so that the mole ratios of fluorine and iodine atoms toammonia were 0.5% and 0.75%, respectively, and the crystal growth timeperiod was changed to 43 days.

Out of this GaN crystal, an M-plane substrate (secondary substrate) wascut, which had rectangular main surfaces having longer sides parallel tothe a-axis and shorter sides parallel to the c-axis, and s size of 27 mm(length)×10 mm (width)×470 μm (thickness). Both of the main surfaceswere subjected to lapping and CMP processing, and a damaged layer formedby slicing was completely removed.

(3) Fabrication of Tertiary Substrate (M-Plane GaN Substrate)

A GaN crystal was grown by the ammonothermal method by using thesecondary substrate fabricated in the above described procedure (M-planeGaN substrate) as a seed. Except that a different seed was used, theadditive amounts of the mineralizers were changed so that mole ratios offluorine and iodine atoms to ammonia was 0.5% and 1.5%, respectively,and the crystal growth time period was 16 days, the GaN crystal for thetertiary substrate was grown in the same procedure as that of the GaNcrystal growth for the secondary substrate.

The size of GaN crystal obtained after the growth was 32 mm (a-axisdirection)×12 mm (c-axis direction)×6 mm (m-axis direction).

Out of this GaN crystal, an M-plane substrate with an off-angle(tertiary substrate) was cut, which had rectangular main surfaces havinglonger sides parallel to the a-axis and shorter sides parallel to thec-axis, and a size of 27 mm (length)×7 mm (width)×330 μm (thickness).The off-angle was set to be −2° in the direction, and within ±0.1° inthe [−12-10] direction. Both of the main surfaces were subjected tolapping and CMP processing, and a damaged layer formed by slicing wascompletely removed.

SIMS analysis of the M-plane GaN substrate determined oxygenconcentration to be 2.3×10¹⁸ cm⁻³. Analysis by the room-temperaturecathode luminescence method (3 kV, 100 pA, 1000-fold magnification) didnot detect basal plane dislocation. Analysis by the low-temperaturecathode luminescence method (10 kV, 4 nA, field of view at 200-foldmagnification, sample temperature 82K) determined the stacking faultdensity of the substrate to be 0 cm⁻¹.

(4) GaN Crystal Growth by HVPE Method

A GaN crystal was grown by the HVPE method by using the tertiarysubstrate fabricated in the above described procedure (M-plane GaNsubstrate) as a seed.

In this example, the susceptor was surmounted by two seed substrateswhich were arranged so that, as depicted in the cross-sectional view ofFIG. 11, the C-plane of the one substrate butted −C-plane of the other.The angle between the a-axises of the respective seed substrates, whenthe susceptor was seen from above, was set to be within 0.5°.

In the GaN crystal growth, the above-mentioned two-stage growth methodwas used. In other words, the seed substrate was placed in the growthfurnace, and then, the substrate temperature was raised up to 850° C.with only N₂ and NH₃ initially fed onto the seed substrate (heatingstep), and the temperature was kept for 15 minutes.

Then, feeding GaCl onto the seed substrate was initiated by feeding HCldiluted with N₂ into the reservoir heated to 800° C. which holdedmetallic gallium, and the substrate temperature was raised at a rate of21° C./min (initial growth step).

After the substrate temperature reached 950° C., the substratetemperature was kept constant while GaN crystal was grown for 72 hoursby feeding GaCl and NH₃ onto the seed substrate (main growth step).

From the start of the heating step to the end of main growth step, thepressure in the growth furnace was controlled to be 1.0×10⁵ Pa, the GaClpartial pressure 3.8×10² Pa and the ammonia partial pressure 1.2×10⁴ Pa.For carrier gasses, N₂ and H₂ were used, and the ratio of N₂ was set soas to account for 48% of the sum of volumetric flow rates of all thegasses fed into the growth furnace.

The grown GaN crystal presented a continuous film extending from the onesubstrate to the other, and the film thickness was about 5.1 mm.

Out of this GaN crystal, an M-plane substrate with an off-angle was cut,which had rectangular main surfaces having longer sides parallel to thea-axis and shorter sides parallel to the c-axis, and a size of 25.5 mm(length)×12.5 mm (width)×354 μm (thickness). The off-angle was set to be−5° in the [0001] direction, and within ±0.1° in the [−12-10] direction.Both of the main surfaces were subjected to lapping and CMP processing,and a damaged layer formed by slicing was completely removed.

For one of the obtained M-plane GaN substrate, basal plane dislocationdensity and stacking fault density in the main surface thereof(corresponding to the part of growth thickness of about 2 mm) weremeasured. The results were a basal plane dislocation density of 3.1×10⁵cm⁻² measured by the room-temperature cathode luminescence method(acceleration voltage 7 kV, electric current 2 nA, 1000-foldmagnification) and a stacking fault density of 1.8 cm⁻¹ measured by thelow-temperature cathode luminescence method (acceleration voltage 7 kV,electric current 2 nA, 200-fold magnification, sample temperature 82K).

Carrier density measured by Raman spectroscopy in the vicinity of themain surface of the M-plane GaN substrate was from 5.8×10¹⁸ to 1.3×10¹⁹cm⁻³.

The carriers were attributed to oxygen incorporated into the GaN crystalduring the vapor phase epitaxy.

3. Experiment 3 (1) Fabrication of M-Plane GaN Substrate

A C-plane GaN template having a single crystalline GaN layer grown on asapphire substrate was prepared by metalorganic chemical vapordeposition (MOCVD) method.

On the GaN layer of the C-plane GaN template, a mask pattern forselective growth was formed, which was composed of a silicon nitridefilm of 80 nm thickness and presented the superposition of a dot patternand a triangular lattice pattern.

For the dot pattern included in the above described superposed pattern,regular hexagonal dots were arranged on the lattice points of the squarelattices formed by unit lattices being a square with each side of 800μm. The square lattices were arranged so that the two sides of thesquare unit lattice were oriented parallel to the a-axis of GaN layerand the other sides parallel to the m-axis thereof. Each of the dots wasarranged so that each of the sides of the regular hexagon was orientedparallel to the m-axis of the GaN layer. The size of each of the dotswas determined so that the distance between the two sides parallel toeach other of the regular hexagon was 100 μm, i.e. the length of each ofthe sides of the regular hexagon was 57.7 μm.

For the triangular lattice pattern included in the above describedsuperposed pattern, the line width of the pattern W was set to be 2 μm,and the height of the triangle formed by line segments connecting theneighboring lattice points was set to be 20 μm. Accordingly, the latticepitch (distance between two neighboring lattice points) P was 23.1 μm.The triangular lattice pattern was arranged so that each of the linescomposing the triangular lattices was parallel to the a-axis of the GaNlayer.

Then, on the above-described C-plane GaN template having the mask forselective growth formed thereon, a GaN crystal was grown by the HVPEmethod. The growth temperature was 965° C. for initial 15 minutes, andthen, raised to 1005° C. The growth pressure was 1.0×10⁵ Pa, the GaClpartial pressure 1.0×10³ Pa, and the NH₃ partial pressure 1.0×10⁴ Pa.The growth time period was 51 hours.

Due to the generation of a facet growth mode, the GaN crystal during thegrowth was doped with oxygen. Oxygen was attributed to oxygen compoundssuch as H₂O incorporated into the feedstock, or to quartz membersconfiguring the vapor phase epitaxy apparatus.

The thickness of the as-grown GaN crystal was 9.9 mm, and the surfacethereof was bumpy, indicating that the facet growth was maintained.

The curvature radius of the (0001) surface of the as-grown crystalexamined by X-ray diffraction analysis was 59 m in the a-axis directionand 13 m in the m-axis direction.

Out of the obtained GaN crystal, an M-plane substrate with an off-anglewas cut, which had rectangular main surfaces having longer sidesparallel to the a-axis and shorter sides parallel to the c-axis, and asize of 30 mm (length)×5 mm (width)×330 μm (thickness). The off-anglewas set to be −5° in the direction, and within ±0.1° in the [−12-10]direction. Both of the main surfaces were subjected to lapping and CMPprocessing, and a damaged layer formed by slicing was completelyremoved.

Basal plane dislocation density in the main surface of this M-plane GaNsubstrate was 8.0×10⁵ cm⁻² by the room-temperature cathode luminescencemethod (3 kV, 100 pA, 1000-fold magnification).

(2) GaN Crystal Growth by HVPE Method

A GaN crystal was grown by the HVPE method by using the M-plane GaNsubstrate fabricated in the above described (1) as a seed.

For the GaN crystal growth, the above-mentioned two-stage growth methodwas used. In other words, the susceptor placed in the growth furnace wassurmounted by the seed substrate so that one main surface of thesubstrate turned up, and then, the substrate temperature was raised upto 850° C. with only N₂ and NH₃ initially fed onto the seed substrate(heating step), and the temperature was kept for 15 minutes.

Then, feeding GaCl onto the seed substrate was initiated by feeding HCldiluted with N₂ into the reservoir heated to 800° C. which holdedmetallic gallium, and the substrate temperature was raised at a rate of21° C./min (initial growth step).

After the substrate temperature reached 950° C., the substratetemperature was kept constant while GaN crystal was grown for 50 hoursby feeding GaCl and NH₃ onto the seed substrate (main growth step).

From the start of the heating step to the end of the main growth step,the pressure in the growth furnace was controlled to be 1.0×10⁵ Pa, theGaCl partial pressure 4.1×10² Pa and the ammonia partial pressure1.3×10⁴ Pa. For carrier gasses, N₂ and H₂ were used, and the ratio of N₂was set so as to account for 48% of the sum of volumetric flow rates ofall the gasses fed into the growth furnace.

The thickness of the obtained GaN crystal layer was about 4.0 mm.

Out of this GaN crystal, a plurality of M-plane substrates with anoff-angle were cut, which had rectangular main surfaces having longersides parallel to the a-axis and shorter sides parallel to the c-axis.The off-angle was set to be −5° in the [0001] direction, and within±0.1° in the [−12-10] direction.

For one of the plurality of the fabricated M-plane GaN substrates,stacking fault density in the main surface (corresponding to the part ofthe growth thickness of about 2 mm) was 27 cm⁻¹ by the low-temperaturecathode luminescence method (acceleration voltage 7 kV, electric current2 nA, 300-fold magnification, sample temperature 82K).

4. Experiment 4 (1) Fabrication of Primary Substrate (C-Plane GaNSubstrate)

Except that the GaCl partial pressure in the growth furnace was set tobe 1.4×10³ Pa and the NH₃ partial pressure 1.1×10⁴ Pa, GaN crystal wasgrown by the HVPE method on the C-plane GaN template having a maskpattern for selective growth thereon in the same manner as that inExperiment 3. (1).

The thickness of the as-grown GaN crystal was 10.1 mm, and the surfacethereof was bumpy, indicating that the facet growth was maintained.

The curvature radius of the (0001) surface of the as-grown crystalexamined by X-ray diffraction analysis was 22 m in the a-axis directionand 191 m in the m-axis direction.

Out of this GaN crystal, a C-plane substrate with 70 mm diameter wascut. The +C-plane was subjected to lapping and CMP processing tocompletely remove a damaged layer formed by slicing.

(2) Fabrication of Secondary Substrate (M-Plane GaN Substrate)

On the +C-plane of the C-plane GaN substrate fabricated in above (1), aGaN crystal was grown by the HVPE method. The growth temperature was1065° C. for initial one hour and 40 minutes, and then, lowered to 1005°C. The growth pressure was 1.0×10⁵ Pa, the GaCl partial pressure 6.3×10²Pa, and the NH₃ partial pressure 7.4×10³ Pa. The growth time period was20 hours in total.

The thickness of the as-grown GaN crystal was 3.0 mm, and the surfacethereof was a mirror surface (C-plane).

Out of the this GaN crystal, an M-plane substrates with an off-angle wascut, which had rectangular main surfaces having longer sides parallel tothe a-axis and shorter sides parallel to the c-axis, and a size of 30 mm(length)×2.5 mm (width)×330 μm (thickness). The off-angle was set to be−5° in the [0001] direction, and within ±0.1° in the [−12-10] direction.Both of the main surfaces were subjected to lapping and CMP processing,and a damaged layers formed by slicing was completely removed.

Basal plane dislocation density in the main surface of this M-plane GaNsubstrate was 1.0×10⁴ cm⁻² or less by the room-temperature cathodeluminescence method (3 kV, 100 pA, 1000-fold magnification).

(3) GaN Crystal Growth by HVPE Method

GaN crystal was grown by HVPE method by using the secondary substratefabricated in the above described (2) as a seed.

For the GaN crystal growth, the above-mentioned two-stage growth methodwas used. In other words, the susceptor placed in the growth furnace wassurmounted by the seed substrate so that one main surface of thesubstrate turned up, and then, the substrate temperature was raised upto 850° C. with only N₂ and NH₃ initially fed onto the seed substrate(heating step), and the temperature was kept for 15 minutes.

Then, feeding GaCl onto the seed substrate was initiated by feeding HCldiluted with N₂ into the reservoir heated to 800° C. which holdedmetallic gallium, and the substrate temperature was raised at a rate of21° C./min (initial growth step).

After the substrate temperature reached 950° C., the substratetemperature was kept constant while GaN crystal was grown for 15 hoursby feeding GaCl and NH₃ onto the seed substrate (main growth step).

From the start of the heating step to the end of the main growth step,the pressure in the growth furnace was controlled to be 1.0×10⁵ Pa, theGaCl partial pressure 4.1×10² Pa and the ammonia partial pressure1.3×10⁴ Pa. For carrier gasses, N₂ and H₂ were used, and the ratio of N₂was set so as to account for 48% of the sum of volumetric flow rates ofall the gasses fed into the growth furnace.

The thickness of the obtained GaN crystal layer was about 1.5 mm.

The stacking fault density of the as-grown GaN crystal was 0 cm⁻¹ fromevaluation by the low-temperature cathode luminescence method (7 kV, 2nA, 300-fold magnification, sample temperature 82K).

5. Experiment 5 (1) Fabrication of M-Plane GaN Substrate

A C-plane GaN template having a non-doped GaN layer epitaxially grown ona sapphire substrate by the MOCVD method was prepared. Then, a maskpattern for selective growth was formed on the surface of the GaN layerby using the silicon nitride film.

The mask pattern was configured to be a stripe pattern (line-and-spacepattern) of 850 μm pitch with 50 μm line width (mask width) and 800 μmspace width, and the stripe was oriented parallel to the direction ofthe m-axis of the single crystalline GaN layer.

On the above-described C-plane GaN template provided with the maskpattern thereon, an undoped GaN layer was laterally epitaxially grown bythe MOCVD method to obtain a seed substrate. On this seed substrate, aGaN crystal was grown by the HVPE method. The growth temperature was1010° C., and the growth pressure was 1.0×10⁵ Pa, the GaCl partialpressure 6.6×10² Pa, and the NH₃ partial pressure 7.6×10³ Pa. The growthtime period was 64 hours.

The thickness of the as-grown GaN crystal was 8.3 mm. Out of this GaNcrystal, an M-plane substrate with an off-angle was cut, which hadrectangular main surfaces having longer sides parallel to the a-axis andshorter sides parallel to the c-axis, and a size of 50 mm (length)×5 mm(width)×330 μm (thickness). The off-angle was set to be −5° in the[0001] direction, and within ±0.1° the [−12-10] direction. Both of themain surfaces were subjected to lapping and CMP processing, and adamaged layer formed by slicing was completely removed.

Basal plane dislocation density in the main surface of this M-plane GaNsubstrate was 5×10⁶ cm⁻² by the room-temperature cathode luminescencemethod (3 kV, 100 pA, 1000-fold magnification).

2) GaN Crystal Growth by HVPE Method

GaN crystal was grown by the HVPE method by using the M-plane GaNsubstrate fabricated in the above described (1) as a seed.

In the GaN crystal growth, the above-mentioned two-stage growth methodwas used. In other words, the susceptor in the growth furnace wassurmounted by the seed substrate, and then, the substrate temperaturewas raised up to 850° C. with only N₂ and NH₃ initially fed onto theseed substrate, and the temperature was kept for 15 minutes. Then,feeding GaCl onto the seed substrate was initiated by feeding HCldiluted with N₂ into the reservoir heated to 800° C. which holdedmetallic gallium, and the substrate temperature was raised at a rate of21° C./min. After the substrate temperature reached 950° C., thesubstrate temperature was kept constant while GaN crystal was grown for30 hours by feeding GaCl and NH₃ onto the seed substrate.

From the start of the heating step to the end of the main growth step,the pressure in the growth furnace was controlled to be 1.0×10⁵ Pa, theGaCl partial pressure 3.5×10² Pa and the NH₃ partial pressure 1.1×10⁴Pa.

The thickness of the obtained GaN crystal layer was about 0.8 mm.

The basal plane dislocation density of the as-grown GaN crystal was1.5×10⁶ cm⁻² by the room-temperature cathode luminescence method (3 kV,100 pA, 1000-fold magnification).

The stacking fault density of the as-grown GaN crystal was 1.5×10² cm⁻¹by the low-temperature cathode luminescence method (5 kV, 500 pA,200-fold magnification, sample temperature 82K).

6. Experiment 6 (1) Fabrication of M-Plane GaN Substrate

Out of the GaN crystal grown on the C-plane GaN template by the samemethod as that in (1) of Experiment 5, an M-plane just substrate(M-plane substrate provided with no off-angle) was cut, which hadrectangular main surfaces having longer sides parallel to the a-axis andshorter sides parallel to the c-axis, and a size of 20 mm (length)×10 mm(width)×330 μm (thickness). Both of the main surfaces were subjected tolapping and CMP processing, and a damaged layer formed by slicing wascompletely removed.

Basal plane dislocation density in the main surface of this M-plane GaNsubstrate was 5×10⁶ cm⁻² by the room-temperature cathode luminescencemethod (3 kV, 100 pA, 1000-fold magnification).

(2) GaN Crystal Growth by Ammonothermal Method

A GaN crystal was grown by the ammonothermal method by using the M-planeGaN substrate fabricated in the above described (1) as a seed.

The condition of the ammonothermal method was the same as that in (2) ofExperiment 1 except that the additive amounts of the mineralizers werechanged so that the mole ratios of fluorine and iodine atoms to ammoniawere 0.2% and 1.5%, respectively, and the number of day period for thegrowth was 9.1 days.

The size of the as-grown GaN crystal was 11 mm (in the c-axisdirection)×20 mm (in the a-axis direction)×1.8 mm (in the m-axisdirection).

A plurality of M-plane substrates were cut out of this GaN crystal. Bothof the main surfaces of the cut substrate were subjected to lapping andCMP processing, and a damaged layer formed by slicing was completelyremoved.

Stacking fault density in the main surface of the M-plane GaN substratewas 1.5×10² cm⁻¹ by the low-temperature cathode luminescence method (5kV, 500 pA, 200-fold magnification, sample temperature 82K).

The results of Experiments 1 to 6 are summarized in Table 1.

TABLE 1 Experiment Experiment Experiment Experiment ExperimentExperiment 1 2 3 4 5 6 seed oxygen 8.7 × 10¹⁸ 2.3 × 10¹⁸ — — — —substrate concentration (cm⁻³) basal plane not not 8 × 10⁵ ≤1 × 10⁴ 5 ×10⁶ 5 × 10⁶ dislocation detected detected density (cm⁻²) GaN oxygen 4.0× 10¹⁸ — — — — — crystal concentration grown on (cm⁻³) seed carrierdensity 2.5 × 10¹⁸ 5.8 × 10¹⁸- — — — — substrate (cm⁻³) 1.3 × 10¹⁹stacking fault not 1.8 27 0 150 150 density (cm⁻¹) detected

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope thereof.

DESCRIPTION OF SYMBOLS

-   1 substrate-   11 main surfaces-   12 edge surface-   2 crystal growth apparatus-   200 growth furnace-   201˜205 introduction pipe-   206 reservoir-   207 heater-   208 susceptor-   209 exhaust tube-   3 crystal growth apparatus-   301 autoclave-   304 platinum wire-   305 baffle-   306 crystal growth zone-   307 seed crystal-   308 feedstock-   309 feedstock dissolution zone-   310 valve-   311 vacuum pump-   312 ammonia tank-   313 nitrogen tank-   314 mass flow meter-   320 growth vessel-   40A semiconductor light-emitting device-   40B semiconductor light-emitting device-   41 GaN substrate-   42 n-type layer-   43 light-emitting layer-   44 p-type layer-   45 positive electrode-   46 negative electrode

1-19. (canceled)
 20. A gallium nitride substrate comprising a first mainsurface and a second main surface opposite thereto, wherein the firstmain surface is a non-polar or semi-polar plane, a dislocation densitymeasured by a room-temperature cathode luminescence method in the firstmain surface is 1×10⁴ cm⁻² or less, and an averaged dislocation densitymeasured by a room-temperature cathode luminescence method in anoptional square region sizing 250 μm×250 μm in the first main plan is1×10⁶ cm⁻² or less.
 21. A gallium nitride substrate according to claim20, wherein the dislocation density is 10 cm² or less.
 22. A galliumnitride substrate according to claim 20, wherein the averageddislocation density is 1×10⁴ cm⁻² or less.
 23. A gallium nitridesubstrate according to claim 20, wherein an area of the first mainsurface is 1.0 cm² or more.
 24. A gallium nitride substrate according toclaim 20, wherein a stacking fault density in the first main surface is10 cm⁻¹ or less.
 25. A gallium nitride substrate according to claim 20,wherein the first main surface is an M-plane.
 26. A gallium nitridesubstrate according to claim 20, wherein the first main surface has anormal vector of which is tilted from <10-10> direction to c-axisdirection, and the normal vector is between <10-11> direction and<10-1-1> direction.
 27. A gallium nitride substrate according to claim26, wherein the normal vector is a direction selected from the groupconsisting of a <30-31> direction, a <30-3-1> direction, a <20-21>direction, a <20-1-1> direction, a <10-11> direction, a <10-1-1>direction, a <10-12> direction, a <10-1-2> direction, a <10-13>direction, a <10-1-3> direction, a <11-21> direction, a <11-2-1>direction, a <11-22> direction, a <11-2-2> direction, a <11-23>direction and a <11-2-3> direction.
 28. A method for manufacturing anitride semiconductor crystal, comprising: growing a nitridesemiconductor crystal on the first main surface of the gallium nitridesubstrate according to claim
 20. 29. The method according to claim 28,wherein in the growing of the nitride semiconductor crystal, the nitridesemiconductor crystal is grown by a vapor phase growth method.
 30. Themethod according to claim 29, wherein the vapor phase growth method isHVPE method.
 31. The method according to claim 30, wherein in thegrowing of the nitride semiconductor crystal, a bulk nitridesemiconductor crystal is grown.
 32. The method according to claim 29,wherein the vapor phase growth method is MOCVD method.
 33. The methodaccording to claim 32, wherein in the growing of the nitridesemiconductor crystal, a thin film of the nitride semiconductor crystalis grown.
 34. The method according to claim 28, wherein in the growingof the nitride semiconductor crystal, the nitride semiconductor crystalgrown directly on the first main surface is a GaN crystal.